Changes in calcium activity (Ca 2ion) will be measured by micro-probes in the extracellular fluid of brain and spinal cord under various physiological and pharmacological conditions. The effect of deliberately varying (Ca 2ion) will be studied in isolated slices of brain and spinal cord tissue. It is expected that from these two sets of experiments it will be possible to determine what role, if any, variations of (Ca2 ion) play in setting the excitability of central neurons, and influencing transmission in synapses of the mammalian nervous system in health and in disease processes. The role of (Ca2 ion) in seizure generation will specifically be examined.